1. Field of the Invention
This invention relates to a method for the production of dithiodialdehydes.
2. Description of the Prior Art
Dithiodialdehydes are useful by themselves as a cross-linking agent and are useful as intermediates for medicines, agricultural pesticides, photographic chemicals, resin improving agents, etc. The mercaptoaldehydes represented by the general formula III: ##STR3## wherein R.sup.1 and R.sup.2 are independently alkyl group of 1 to 8 carbon atoms, are easily obtained by the reduction of dithiodialdehydes. The tertiary thiol group-containing amines represented by the general formula IV: ##STR4## wherein R.sup.1 and R.sup.2 have the same meanings as defined above and R is hydrogen or alkyl group of 1 to 24 carbon atoms are easily obtained by causing various primary amines to react on dithiodialdehydes thereby producing corresponding Schiff bases and subsequently reducing the Schiff bases. The compounds represented by these formulas III and IV are also useful as intermediates for medicines, agricultural pesticides, photographic chemicals, resin improving agents, etc.
The method for producing dithiodialdehydes represented by the general formula II: ##STR5## wherein R.sup.1 and R.sup.2 are independently alkyl group of 1 to 8 carbon atoms, by condensing active hydrogen-containing aldehydes represented by the formula I: ##STR6## wherein R.sup.1 and R.sup.2 have the same meanings as defined above, with sulfur monochloride has been disclosed in U.S. Pat. No. 2,580,695, for example. This condensation is carried out by dissolving in an inactive solvent an active hydrogen-containing aldehyde, one of the two raw materials for the reaction, and then adding sulfur monochloride, the other raw material, to the resultant solution.
By experimentally repeating this method, we have learnt that this method gives the product in a low yield of the order of 50 to 60%. On analysis by gas chromatography, the product of this reaction is found to contain various impurities which are thought to be decomposition products of aldehyde. An increase in the time spent for the addition of sulfur monochloride has been found to lower the yield of the reaction and the purity of the product. Since this reaction is highly exothermal, the control of the reaction temperature necessitates exact control of the speed of addition of sulfur monochloride. A method of such a nature cannot be effectively carried out on a commercial scale to obtain the product with highly stable yield and purity.
An object of this invention, therefore, is to provide an improved method for the production of a dithiodialdehyde.
Another object of this invention is to provide an economically advantageous method capable of producing a dithiodialdehyde in a high yield with a high purity without entailing the aforementioned drawbacks suffered by the conventional method.